Enterprise Networking And Ring Topology Computer Science Essay

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This topology works when a node is connected to exactly two other nodes in the network forming a continual path for dataflow through each node, forming a ring.

Since the availability of each node is vital to the network, the failure of a connection can bring the whole network down. Because of this, many ring networks send data over a second ring forming a redundant link or a 'dual-ring' network. Such is the technology of FDDI.

The most common type of network, this layout consists of a central device (hub, switch or computer) that is the intermediary for transmitting data to the other nodes.

Unlike the ring, failure of one node does not bring the whole network down; but if the central device fails, then be ready for some downtime.

The simplest type of network, the clients are connected together using a shared line or link called a bus.

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Though it is simple, since the line is shared, the bandwidth reduces drastically when additions are made to the network. But the biggest problem is when two clients transmit data signals at the same time. This is when data collisions take place and data loss occurs.

This is the most redundant yet equally complicated of all the four mentioned. It works on the principle of 'everything connected to everything' and taking it to its literal sense. All nodes are connected to each other via a point-to-point link. A broken link or two will not affect the connectivity of this network.

Though it sounds quite intriguing, laying the cables is an expensive and a strenuous task and is not feasible for large networks.

Two types of media can be used for both topologies:

Twisted Pair cable (TP)

This type of cable consists of many pairs of wires with each individual twisted around the other in the pair. This is done to cancel the electromagnetic interference (EMI) from external sources and crosstalk between adjacent pairs.

The most famous type of TP cable is the Unshielded TP (UTP). They are found in many Ethernet networks and telephone lines.

Fibre optic cable (FoC)

This cable contains one or more optical fibres.

Cable Type

Advantages

Disadvantages

Twisted Pair cable (TP)

Thin and flexible cable, can run through walls easily

Cheap

Defence against EMI greatly depends on the number of twists per foot; less twists, lower defence

Low range, maximum of 100m.

Fibre optic cable (FoC)

Immune to EMI

Very high bandwidth with a range up to 10km.

Very expensive.

In conclusion, looking at the types of networks and the media, the best options for the fire department is a star Ethernet network over Unshielded Twisted Pair (UTP) cables.

Task Two

The fire department will require an internet connection for three main purposes:

Web browsing

As the name says, employees will need to browse the web, for personal or professional reasons. Most operating systems support this service, with web browsers built into them.

Web publishing

This service will be used to host the fire department's internal and/or external websites.

Email/messaging

Looking at the above internet requirements, the following assumptions can be made:

All employees will not be browsing and/or reading their emails at the same time

Web publishing will require a dedicated broadband connection, so that the public can contact the fire department, make complaints and report fires through its online service (assuming they have that functionality) without suffering any webpage errors.

Therefore, employees will need a 1 Mbps connection, while the web server will require another connection of the same bandwidth (1 Mbps) for itself.

Two service providers can provide this service, Du and Etisalat, both of which price their services at same levels. Since Etisalat has been operating for a long time, they have a much stronger infrastructure therefore they are a good choice.

Task Three

Technologies for communication

For communication purposes, the Fire Department can use a 'Two-way Radio'. A two-way radio is a radio that can both transmit or receive radio signals (also known as a transceiver). These are available in mobile, stationary-base and portable hand-held configurations. The hand-held ones are often called walkie-talkies. All these come with a push-to-talk button, which is used to initiate the communication.

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Two-way radio systems can be applied in many situations like in aviation or the marines; the following are examples of lad-based radio systems:

Professional Mobile Radio (PMR)

Also known as Private Mobile Radio (PMR) in the UK and Land Mobile Radio (LMR) in North America, this uses portable, base stations and dispatch console radio systems. This type of system is commonly used in police departments. Important features of PMR include:

Point to multi-point communication

Push-to-talk system, where a button initiates the communication; indicates that it is half-duplex

Large coverage areas

Closed user groups

Uses VHF or UHF frequency bands

Each user has a dedicated frequency for communication

Trunked radio systems

Also known as Public Trunked Mobile Radio (PTMR), it was designed to overcome the disadvantages of the Professional Mobile Radio (PMR). Though most of the features are similar between PMR and PTMR, the only difference between them is that PTMR does not require the person to have a dedicated frequency for communication.

Trunked radio systems are used because they can have virtually unlimited users over fewer frequency bands. Some PTMR radio equipment have data ports, allowing data to be transmitted over the network.

Global System for Mobile Communications (GSM)

This is the most popular standard for mobile communications. It works by means of searching for cells around the area. There are five different cells sizes in a GSM network. The coverage area of each cell depends on the implementation and environmental factors. The radius of the cell depends on the antenna height, propagation and antenna gain.

GSM operates in the following frequency bands:

850Mhz

900MHz

1800MHz

1900MHz

Each GSM mobile device requires a Subscriber Identity Module, most commonly known as a SIM card. This card is detachable and contains the user's subscription information and a phone book.

GSM provides two-way communication (full-duplex)

Short Messaging Service (SMS) is also provided; this allows sending short text-based messages to handsets

Data-transfer speeds are clocked at 9.6Kbits/second.

As a response to this mediocre data rates, general Packet Radio Service (GPRS) was introduced to take advantage of the current GSM network and provide a much higher data rate ranging from 14Kbits/second to 112Kbits/second. This in turn allows for reasonable Internet access because GPRS uses an IP backbone.

GPRS also supports Quality of Service (QoS) and this ensures adequate bandwidth availability.

Legal requirements

The Telecomm Regulatory Authority (TRA) in this country provides an extensive and comprehensive document on the legal requirements regarding PMR and GSM networks.

For frequency spectrum authorization, the applicant should do the following [1] :

Fill an application form (soft or hard copy)

Any technical details that might be required by the TRA

Copy of a valid commercial license or official letter of registration

Proof of payment for processing the application (an amount that equals 500 Dirhams)

Applicant should use the equipment that meets the TRA's standards

Applicant will apply for the minimum spectrum resource required

This authority to use the frequency is normally valid for one year and can be valid for a period of up to five years, which is when the holder of the frequency will be asked to renew his authorization. [2] 

The annual spectrum fees for Public Land Mobile (cellular services including GSM, UTMS and IMT) is [3] :

[FF * CF * P * BW] / 4000

Where:

FF is the Frequency Factor

CF is the Coverage Factor

P is the price per MHz (currently at 978,560 Dirhams)

BW is the bandwidth assigned in MHz

The annual spectrum fees for PMR, Paging, PTMR in the frequency range of 30MHz - 700MHZ is [4] :

NC * CF + SUM(WE * 500 * PF)

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Where:

NC is the number of channels that will be assigned

WE is the number of wireless equipment that will be included

PF is the power factor of the device

CF is the coverage factor

SUM(WE * 500 * PF) is the sum of all wireless equipment multiplied by 500 multiplied by the power factor of each device

Installation and licensing cost

The costs that will incur during setting up and running the equipment are:

Purchasing the equipment

Obtaining licences for the frequencies that will be used

The licencing costs will depend on a number of factors such as the number of frequency bands that will be used, the number of channels that will be assigned, range, etc.

Maintaining the equipment

This will include costs of operation, the people employed to take care and run the equipment, repairs that might need to take place, electricity and so on.

Limitations of the methods described previously:

PMR/PTMR

GSM

Radio systems must be in effective range over each other

Channel bandwidth limits number of simultaneous conversations

Communication is not encrypted for PMR but it is in PTMR hence eavesdropping PMR networks is easy

Only one-way communication is possible

Other radio devices might interfere with the signals, example mobile phones

Data transfer rates are slow

Expensive to create a new GSM network

Signals are not encrypted

Encryption mechanisms for GSM networks are very expensive

If an existing carrier network is used, data transfer rates are high but so is the cost

Recommendation:

Though GSM networks provide full duplex communication with faster data rates, PMR is still a better choice because it is relatively inexpensive to setup and operate and provides just enough functionality for the Fire Department to keep in touch with their mobile units.

Task Four

Three vendors; Panasonic, NEC and Siemens were selected as providers for a PABX system. The features and cost are as follows:

Panasonic KX-NPC500

NEC Univerge SV8100

Siemens HiPath 3350

Features

VoIP

156 max extensions

20 single line telephones

128 max IP phones

64 max portable handsets

VoIP

96 BRI and 46 PRI channels

104 physical ports

Voicemail

16-bridge multimedia conference

8 portable handsets

VoIP

96 max IP phones

36 single line phones

16 portable handsets

Voicemail

Wall-mountable

Price

$1,110

$2,180

Recommendation:

The NEC Univerge is a good option because it supports Voicemail, ISDN, multimedia conferencing (audio and video) and more than enough ports for the employees. It is also modular, which means adding additional units for phone lines is easy when it is time for an upgrade.

Task Five

For a sector such as the Fire Department, it is crucial that it stays alive no matter what the situation, whether it be a power outage, a natural disaster, communications going down etc. and there should always be a backup plan in the case that any of these happen. The list below is by no means exhaustive, but does contain a few measures that can be put in place:

Service disruption

UPS, Generators, Solar Panels

Each server, radio base station and telephone exchange should be connected to an Uninterrupted Power Supply, or a generator or a battery connected to a solar panel. There are no restrictions on how many of these can be used. This will ensure that communication is not hindered.

All data centres should have specifications against fires and terrorist attacks.

Communication disruption

If data must be transferred, the Fire Department can use satellite or GSM networks. They might not have their own GSM network, so they can use the carrier network to ensure on-going communication.

Fax machines should be preprogramed to divert calls.

Natural/Unnatural disasters

As mentioned above, all data centres must have specifications against fires or terrorist attacks. Natural disasters cannot be avoided but the risk can be reduced. As such, if there comes a point that something should happen, all data held within the servers must be backed up and stored in a different location altogether. This will mitigate data loss and recovery will be relatively easier.